Fix complex_filter on Linux

[Petr Nejedly]

Looks like filter separator cannot be escaped, and we should use quotes aroud the filter string.

Example:

ffmpeg -threads auto -i /home/matteo/Video/Mistress.America.2015.HDRip.XviD.AC3-EVO/Mistress.America.2015.HDRip.XviD.AC3-EVO.avi -y -threads auto -c:v mpeg2video -pix_fmt yuv420p -b:v 17000k -maxrate:v 17000k -bufsize:v 17000k -filter_complex "[0:0]subtitles=filename='/home/matteo/Video/Mistress.America.2015.HDRip.XviD.AC3-EVO/Mistress.America.2015.HDRip.XviD.AC3-EVO.srt':original_size=720x384:charenc=UTF-8[v1];[v1]pad=720:405:0:10:black[v2];[v2]setdar=4:3[v]" -r 24000/1001 -g 15 -c:a copy -map [v] -map 0:1 -sn -f mpegts /tmp/test.mpg

[Petr Nejedly]

quotes around filter definition, no need for quotes around subtitles filename, always use semicolon for filter separation